Given your location, damp, and mild but cool, here are some unusual NZ/Aus and Chilean plants you can try, which will do well for you but not for many other people, provided you aren't by some unfortunate chance on a limey soil. Many of these are known to do well in mild coastal locations in N Ireland, provided they aren't wind-blasted by salt spray.

Chilean Holly: Desfontainea Spinosa. Has a leaf just like a holly but exotic yellow/red tubular flowers in summer/autumn.

Luma apiculata (or Myrtus luma) has lovely myrtle type flowers then berries. When mature its bark is lovely. Also a variagated form Glanlean Gold, but doesn't tend to have the bark.

Tasmanian pepper: Drimys lanceolata (recently renamed Tasmannia lanceolata, but rarely seen under that name). Interesting spring flowers. Red leaf stems make a nice contrast with the green leaf. You need male and female plants to get the seeds, which can be used as pepper seeds (very cool). Maybe Winter's Bark (Drimys winteri) will also grow for you.

Chilean Fire bush: Embothrium coccineum wonderful display of red flowers in late spring.

Chilean Lantern bush: Crinodendron hookerianum: extraodinary hanging fuschia-coloured lantern like flowers.

Philesia magellanica: Just like the much sought after flowers of the climber lapageria rosea, but on a shrub few people can grow.

Chilean fern tree: Lomatia ferruginea, large fern-shaped leaves with intriguing exotic orange flowers

Chilean hazelnut: Gevuina avellana - huge compound leaves with exotic white flowers and very desirable macadamia-like nuts that take a year to mature on the tree, though I think you'll need an unusually warm summer for the nuts to develop. They do well in Devon.

Chilean cranberry: Ugni molinae. Similar to myrtle. Was Queen victoria's favourite berry and cultivated in Cornwall for her, but you'll have to be frost free through till about early December to get ripe fruit though.

New Zealand Flax: Phormium spp, comes in all sorts of colours these days with exotic flowers.

Kowhai: Sophora tetraptera and Sophora microphylla, the national tree of New Zealand, very showy yellow flowers cover the tree in early spring, delicate mimosa-like leaf, can be defoliated in a cold winter. Then long seed pods.

Lacebark: Hoheria sextylosa, covered in white fragrant flowers in July/August when most things aren't. Avoid Glory of Amlwch because it tends to be a shapeless lump when not in flower. Can lose leaves in a cold winter.

Barbed-wire bush: Colletia spp (two distinct types and a lot of confusion over the names) has vicious thorns rather than leaves, but covered in very aromatic flowers that smell of vanilla custard in summer.

Grevillea rosemarinifolia: a bit like rosemary with longer needles, and very exotic red flowers over a long period.

Banksia: probably B. spinulosa, B. ericifolia and B. integrifolia will grow for you, strange flowers like a cross between a pinecone and feather duster. It becomes a large seedpod which is used for various craft purposes. Interesting leaf too on some of them.

Mayten tree: Maytenus boaria unusual small evergreen tree, well known at Portmeirion that place with the pottery where they filmed The Prisoner near Porthmadoc. Also Maytenus magellanica, very hardy and wind tolerant, has been grown in the Faroes.

And don't forget Rhododendrons/Azaleas, many of them are evergreen. And hebes. And olearias. etc.